Bonding mechanism of ultrasonic wedge bonding of copper wire on Au/Ni/Cu substrate
(1. State Key Laboratory of Advanced Welding Production Technology, Harbin Institute of Technology,Harbin 150001, China;2. Microjoining Laboratory, Center for Advanced Materials Joining, University of Waterloo,Waterloo, Canada, N2L 3G1)
Abstract: The ultrasonic wedge bonding with d25 μm copper wire was achieved on Au/Ni plated Cu substrate at ambient temperature. Ultrasonic wedge bonding mechanism was investigated by using SEM/EDX, pull test, shear test and microhardness test. The results show that the thinning of the Au layer occurs directly below the center of the bonding tool with the bonding power increasing. The interdiffusion between copper wire and Au metallization during the wedge bonding is assumed negligible, and the wedge bonding is achieved by wear action induced by ultrasonic vibration. The ultrasonic power contributes to enhance the deformation of copper wire due to ultrasonic softening effect which is then followed by the strain hardening of the copper wedge bonding.
Key words: copper wire; ultrasonic wedge bonding; bonding mechanism; wear action